This invention relates to electrochemical cell frames, and especially relates to an electrochemical cell frame having an integral protector portion.
Electrochemical cells are energy conversion devices, usually classified as either electrolysis cells, fuel cells or batteries. The typical proton exchange membrane electrochemical cell stack includes a number of individual cells arranged in a stack with fluid (typically water) flowing therein. The fluid is typically forced through the cells at high pressures.
The cells within the stack are sequentially arranged and include an anode, a proton exchange membrane, and a cathode. The anode/membrane/cathode assemblies are supported on either side by layers of screen or expanded metal, which are in turn surrounded by cell frames and separator plates to form reaction chambers and to seal fluids therein. The cell frames are typically held together in the stack by tie rods passing through the frames and separator plates. End plates are mounted to the outside of the stack, and, together with the cell frames and tie rods, function to counteract the pressure of the fluids operating within the stack.
The frames include ports to communicate fluids from a source to the individual cells and also include additional ports to remove the fluids from the cells. Screens are used to establish flow fields within the reaction chambers. The flow fields facilitate fluid transport, maintain membrane hydration, provide mechanical support for the membrane, and provide a means for transferring electrons to and from electrodes.
A proton exchange membrane electrolysis cell, for example, functions as a hydrogen generator by electrolytically decomposing water to produce hydrogen and oxygen gas. Referring to FIG. 1, in a typical single anode feed water electrolysis cell 101, process water 102 is reacted at oxygen electrode (anode) 103 to form oxygen gas 104, electrons, and hydrogen ions or protons 105. A portion of the process water containing some dissolved oxygen gas 102xe2x80x2, and oxygen gas 104, exit the cell. The protons 105 migrate across a proton exchange membrane 108 to a hydrogen electrode (cathode) 107, where the protons 105 react with the electrons, which have migrated through the electrical load 106, to form hydrogen gas 109. The hydrogen gas 109 and the water 102xe2x80x3 that has been drawn across the membrane 108 by the protons (hydronium ions), exit from the cell through manifolds in the cell stack. Reactions for a typical electrolysis cell are as follows:
Anode: 2H2Oxe2x86x924H++4exe2x88x92+O2 
Cathode: 4H++4exe2x88x92xe2x86x922H2 
A typical fuel cell operates in the reverse manner as that described herein above for electrolysis cells. In a fuel cell, hydrogen, methanol, or other hydrogen fuel source combines with oxygen, via the assistance of a proton exchange membrane, to produce electric power. Reactions for a typical fuel cell are as follows:
Anode: 2H2xe2x86x924H++4exe2x88x92
Cathode: 4H++4exe2x88x92+O2xe2x86x922H2O
The cell frames that surround each of the cells within a stack typically contain multiple ports for the passage of reactant fluids. These ports are usually sealed by means of sealing ridges, which are embossed, machined, or molded into the frame. The sealing features react against gaskets included in the stack to maintain fluid tight joints and also grip the gaskets to prevent creep and extrusion of the membrane. As is well-known in the art and discussed in U.S. Pat. No. 5,441,621 to Molter et al., a common method of sealing utilizes ridges in concentric patterns around the ports, with separate concentric patterns around the sealing area of the cell frame.
A common method for providing a fluid communication pathway between the reservoir, or active area, of a cell and the individual fluid ports in the frame comprises manifolds machined into the frame. The manifolds typically comprise holes machined in the edge of the cell frames orthogonal to the ports. Fluids, after passing through the inlet ports and the holes in the manifolds, enter the screen packs, electrodes, and membrane. The fluids and gas products similarly exit through outlet manifolds and sealed outlet ports to collection tanks.
Existing cell frames have a number of drawbacks and disadvantages. For example, current technology uses protector rings to bridge the gap between the cell frame and the screen packs. The protector rings, which are typically positioned about the perimeter of the frame, function to prevent membrane extrusion and xe2x80x9cpinchingxe2x80x9d between the frame and the screen. Although these protector rings function well in operation, they render assembly of the cell very difficult, often breaking loose, which results in misalignment and possible damage to the membrane. Specifically, because of their small cross-section, the protector rings tend to slide out of position and, as a result, often do not cover the gap between the frame and the screen that they are designed to bridge.
Accordingly, there remains a need in the art for electrochemical cell frames that enable simplified assembly and manufacture, and offer a smooth interface with the membrane.
The present invention relates to an electrochemical cell frame and to an electrochemical cell stack. The electrochemical cell frame comprises: fluid transportation conduits; and an integral protector portion having an extension protruding from the membrane side of the frame.
The electrochemical cell stack comprises: a membrane disposed between an anode electrode and a cathode electrode to form a membrane assembly; at least two screen assemblies; and at least two cell frames, each cell frame having a membrane side and a screen assembly side, and at least one of said frames having an integral protector portion with an extension protruding from the membrane side of the frame; wherein the membrane assembly is disposed between the cell frames, in intimate contact with the membrane side of the cell frames, and one of the screen assemblies is disposed on each of the screen assembly sides of said cell frames, in intimate contact with both of the integral protector portion and the membrane assembly.
The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.